Flavonoid compounds are present in all aerial parts of plants, with high concentrations found in the skin, bark, and seeds. Such compounds are also found in numerous beverages of botanical origin, such as tea, cocoa, and wine. The flavonoids are a member of a larger family of compounds called polyphenols. That is, these compounds contain more than one phenol group (OH) on the respective benzene ring. The physical and chemical properties, nomenclature, analysis and biological activities of polyphenols and particularly flavonoids have been studied for many years.
Proanthocyanidins are a particular class of colorless flavonoid compounds with a general structure as follows: ##STR1##